1. Field of the Invention
The present invention relates to fabrics used in papermaking machines, and, more particularly, to fabrics used to carry fiber or, more particularly, paper webs through a drying press. The present invention is particularly advantageous for tissue paper.
2. Description of the Related Art
For many years attempts have been made to use external air pressure to force water out of a paper web. Rather than compress a sheet at a press nip to the point where hydraulic pressure drives water out, as is the case in normal wet pressing, it was reasoned that more water could be removed, and sheet bulk could be maintained, if air pressure could be applied to supplement roller nip generated hydraulic pressures. One such attempt involves providing a multi-roller or other structure forming an air press having a closed chamber, wherein air is circulated through the chamber to convect moisture out of the paper web. Such air presses typically carry the paper web sandwiched between an upper pressing fabric and a lower anti-rewet layer.
Much attention has been given to the design of the pressing fabric and its characteristics. The construction of the pressing fabric has been thought to be the most important of the above-mentioned fabrics since it controls mechanical pressure on the paper web and the air flow therethrough. However, experimentation has shown the importance of the underneath anti-rewet layer. It has been found that rewet can have a profound effect on sheet solids after pressing. Specifically, the quality of the paper web has been found to decrease with increasing rewet. Sheet rewet can be controlled by the design of the anti-rewet layer.
What is needed in the art is an anti-rewet layer for use in air presses which can effectively minimize the amount of rewet which occurs in a fiber web during and after pressing thereof in a drying press.